Glutamine synthetase cascade: Enrichment of uridylyltransferase in Escherichia coli carrying hybrid ColE1 plasmids

Abstract

We have used hybrid ColE1 plasmids that carry small selected segments of the Escherichia coli chromosome ( L. Clarke and J. Carbon, 1976 Cell 9, 91–99 ) to obtain increased levels of two of the components involved in the covalent modification of glutamine synthetase. Screening of the plasmid collection for those strains capable of correcting the glutamine requirement in glnD mutants of E. coli which lack uridylyltransferase activity indicated that two of these plasmid-containing strains, JA200/pLC 6–32 and JA200/pLC 38–39, overproduce Uridylyltransferase by 14- to 25-fold. In both of these strains the increase in uridylyltransferase levels was correlated with a parallel increase in uridylyl-removing enzyme levels. This is in agreement with evidence which suggests that both of these activities may be encoded by the same or closely neighboring genes. Two plasmids (pLC 28–36 and pLC 41-35), that complement strains with mutations in the glnA gene, the structural gene for glutamine synthetase, are also capable of complementing the defect in the glnD mutants. However, as shown here, this occurs by a mechanism other than overproduction of uridylyltransferase.